1. Field of the Invention
The present invention relates to a vacuum gauge state detection method and a vacuum gauge state detection system for detecting the state of a capacitance vacuum gauge including a movable portion, such as a diaphragm, which senses pressure.
2. Description of the Related Art
In a capacitance diaphragm gauge, a diaphragm, which is a movable portion, senses pressure, and a deflection of the diaphragm caused by pressure is converted to a capacitance value. Such a diaphragm gauge has a small dependence on gas type, and therefore, is commonly used in industrial applications, such as facilities for manufacturing semiconductor devices (see Masashi Sekine, Takuya Ishihara, Nobuo Sashinami, Takeo Tani “Development of the Sensor Chip and Package for a High-Temperature Sapphire Capacitance Diaphragm Gauge”, Azbil Technical Review, pp. 28 to 33, Issue January 2011).
The diaphragm gauge described above includes a base 301, a diaphragm 302, and a pneumatic chamber 303, as illustrated in FIG. 6. The base 301 is formed of an insulator. The diaphragm 302 is formed of an insulator. The diaphragm 302 is supported by a support 301a of the base 301, spaced apart from the base 301 in a movable region 302a of the diaphragm 302, and displaceable in the movable region 302a toward the base 301. The diaphragm 302 senses pressure from a measurement target. The pneumatic chamber 303 is formed between the movable region 302a of the diaphragm 302 and the base 301. Each portion is formed of sapphire.
The diaphragm gauge further includes a movable electrode 304 formed in the movable region 302a of the diaphragm 302, and a fixed electrode 305 formed on the base 301 so as to face the movable electrode 304. The diaphragm gauge further includes a movable reference electrode 306 formed in the movable region 302a of the diaphragm 302 around the movable electrode 304, and a fixed reference electrode 307 formed on the base 301 around the fixed electrode 305 so as to face the movable reference electrode 306.
The diaphragm gauge formed as described above is attached to a pipe, for example, through which a measurement-target gas flows to measure pressure. In the capacitance diaphragm gauge, a deflection of the diaphragm subjected to pressure is converted to a capacitance value. The capacitance diaphragm gauge has a small dependence on the type of gas used, and therefore, is widely used in industrial applications, such as facilities for manufacturing semiconductor devices as described above.
A diaphragm gauge that is used for a film deposition apparatus or an etching apparatus used in manufacture of semiconductor devices is required to have resistance to corrosion caused by a material gas or a cleaning gas, resistance to a by-product deposited during a process, and thermal resistance to a heated pipe. The diaphragm gauge is further required to have durability at the time of maintenance.
A film deposition apparatus or an etching apparatus has a vacuum chamber that is exposed to the atmosphere at the time of maintenance. At this time, an excessive pressure higher than the atmospheric pressure is applied to the diaphragm gauge. Because of stress relaxation, for example, of the diaphragm that is subjected to pressure, the zero-point output value of the diaphragm gauge often changes (hereinafter referred to as “zero-point shift”). Such a change in the output value is caused not only by the stress relaxation but may be caused also by a change in the state of a film deposited on the diaphragm as a by-product produced during a process.
As a measure against the zero-point shift, an adjustment is made commonly by electrically resetting the zero point of the diaphragm gauge. Such an adjustment is currently made on the basis of the user's judgment about the necessity for an adjustment. However, in a case where such an adjustment operation is beyond an allowable adjustment range, the operation is no longer possible and the diaphragm gauge needs to be replaced, which requires the apparatus of interest to be unexpectedly stopped for replacement. Further, it is difficult for the user to predict a frequency and timing at which a zero-point adjustment needs to be made.
As a measure against application of an excessive pressure, a valve may be provided between the diaphragm gauge and the vacuum chamber, and the valve may be closed at the time of maintenance in which an excessive pressure is applied so as to prevent the atmospheric pressure from being applied to the diaphragm gauge. However, this measure is not desirable in terms of both a fail-safe aspect and costs for valve installation.
The allowance of the zero-point shift is specified in advance in the specifications of the diaphragm gauge, and therefore, it is necessary to detect a sign of deterioration caused by application of an excessive pressure or deposition of a by-product. If such a sign is detectable, planned preventive maintenance can be performed, and maintenance need not be frequently performed, which contributes to a reduction in the facility maintenance costs.
In order to detect deterioration (zero-point shift) of a diaphragm gauge, a configuration is currently employed in which an amount of bias adjustment at the time of a zero-point adjustment is monitored, and alarm information is issued from a measurement circuit if the total amount of bias adjustment exceeds a certain threshold. Then, replacement or maintenance of the diaphragm gauge is performed commonly on the basis of the user's judgment about the necessity for replacement or maintenance by referring to a level indicated by the alarm information or an offset amount of the output value of the diaphragm gauge at the time of return to the zero point. Determination as to whether the diaphragm gauge has been appropriately maintained is left to the user's judgment, and therefore, an adjustment may be beyond the allowable adjustment range for the zero point, and the diaphragm gauge may become non-usable.
As the technique for automatically adjusting the zero point of a diaphragm gauge, a technique is available in which the time when inspection or replacement needs to be performed is predicted on the basis of information about the time when a zero-point adjustment was made to thereby automatically perform calibration (see Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-525324). The information based on which prediction is made is collected at the time when the user makes a zero-point adjustment, and may vary depending on the frequency of zero-point adjustment, that is, depending on the user's action and judgement. Further, in a case where the frequency of use of the facility of interest changes or in a case where different process conditions coexist, the precision of prediction of the time may decrease. The time when a zero-point adjustment was made needs to be checked, and therefore, even if subsequent calibration can be automatically performed, a manual operation still needs to be performed by the user.